Coupling control in side-polished fiber devices

• US 6,542,663 B1
• Filed: 09/07/2001
• Issued: 04/01/2003
• Est. Priority Date: 09/07/2000
• Status: Expired due to Term

• Current Assignee: Intelligent Fiber Optic Systems Corporation
• Original Assignee: Oluma, Inc. (Intelligent Fiber Optic Systems, Inc.)
• Inventors: Pi, Bo, Zhao, Shulai
• Primary Examiner(s): Uliah, Akm E.
• Assistant Examiner(s): Doan, Jennifer
• Application Number:
  US09/949,070
• Time in Patent Office: 571 Days
• Field of Search: 385/15, 385/18, 385/30, 385/31, 385/32, 385/39, 385/50, 385/65, 385/83
• US Class Current: 385/30
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/266 the optical element being an attenuator
• CPC Class Codes: G02B 6/2804 forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
• CPC Class Codes: G02B 6/2826 using mechanical machining means for shaping of the couplers, e.g. grinding or polishing grinding, polishing in general B24
• CPC Class Codes: G02B 6/2852 using tapping light guides arranged sidewardly, e.g. in a non-parallel relationship with respect to the bus light guides (light extraction or launching through cladding, with or without surface discontinuities, bent structures)
• CPC Class Codes: G02B 6/29332 Wavelength selective couplers, i.e. based on evanescent coupling between light guides, e.g. fused fibre couplers with transverse coupling between fibres having different propagation constant wavelength dependency non wavelength-selective light guide couplers G02B6/28
• CPC Class Codes: G02B 6/29334 Grating-assisted evanescent light guide couplers, i.e. comprising grating at or functionally associated with the coupling region between the light guides, e.g. with a grating positioned where light fields overlap in the coupler
• CPC Class Codes: G02B 6/29355 Cascade arrangement of interferometers
• CPC Class Codes: G02B 6/30 for use between fibre and thin-film device
• CPC Class Codes: G02B 6/3502 involving direct waveguide displacement, e.g. cantilever type waveguide displacement involving waveguide bending, or displacing an interposed waveguide between stationary waveguides
• CPC Class Codes: G02B 6/3536 involving evanescent coupling variation, e.g. by a moving element such as a membrane which changes the effective refractive index mode converters G02B6/14; adjustable lateral coupling between waveguides G02B6/283; electro- optical refractive index variations G02F1/0118
• CPC Class Codes: G02B 6/356 in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links switching polarized beams G02B6/3594; power equalizers G02B6/356 and G02B6/3594; path selecting means H04Q11/0001
• CPC Class Codes: G02B 6/3582 Housing means or package or arranging details of the switching elements, e.g. for thermal isolation
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C
• CPC Class Codes: G02B 6/3636 the mechanical coupling means being grooves G02B6/3652 takes precedence
• CPC Class Codes: G02B 6/3692 with surface micromachining involving etching, e.g. wet or dry etching steps surface micromachining involving subtractive techniques B81C1/00055

Abstract

Fiber optical devices formed on substrates fabricated with grooves that operate based on evanescent optical coupling through a side-polished fiber surface in each fiber involved. The fiber cladding under the side-polished fiber surface is designed to support a radial mode profile wider than a radial mode profile supported by adjacent fiber portions.

Claims

1. A device, comprising:

a first substrate having a first elongated groove formed over a first substrate surface;

a first fiber having a fiber coupling portion engaged in said first elongated groove, a portion of fiber cladding of said fiber coupling portion being removed to form a first side fiber surface spaced from a fiber core of said first fiber within a reach of an evanescent field of a guided mode in said first fiber;

a second substrate having a second elongated groove formed over a second substrate surface, said second substrate facing said first substrate surface to align said second elongated groove with said first elongated groove;

a second fiber having a fiber coupling portion engaged in said second elongated groove, a portion of fiber cladding of said fiber coupling portion being removed to form a second side fiber surface spaced from a fiber core of said second fiber and within a reach of an evanescent field of a guided mode in said second fiber, said second side fiber surface being within a reach of said evanescent field of said guided mode in said first fiber,

wherein said fiber coupling portion in said first fiber has a fiber cladding portion whose radial index distribution is different from adjacent fiber portions to produce a radial mode profile wider than a radial mode profile of said adjacent fiber portions.

2. The device as in claim 1, wherein a difference between a core refractive index and a cladding refractive index at a boundary of a core and a cladding in said fiber coupling port is less than a difference between a core refractive index and a cladding refractive index at a boundary of a core and a cladding in said adjacent fiber portions.

3. The device as in claim 2, wherein said difference between a core refractive index and a cladding refractive index at a boundary of a core and a cladding in said fiber coupling port changes gradually with a position along said fiber.

4. The device as in claim 1, further comprising an optical grating formed in said first fiber coupling portion.

5. The device as in claim 4, wherein said grating is formed in a fiber cladding.

6. The device as in claim 4, wherein said grating is formed in a fiber core.

7. The device as in claim 4, further comprising a buffer layer between each fiber and a respective substrate to reduce a stress between said each fiber and said respective substrate.

8. The device as in claim 1, wherein said fiber coupling portion in said second fiber has a fiber cladding portion whose radial index distribution is different from adjacent fiber portions to produce a radial mode profile wider than a radial mode profile of said adjacent fiber portions.

9. The device as in claim 1, wherein one of said first and said second substrates includes a through hole between said first substrate surface and a second, opposing substrate surface that penetrates through said substrate, said through hole located at one end of a respective elongated groove and one section of a respective fiber passing through said through hole to place another section of said fiber over said second substrate surface.

10. A method, comprising:

selecting a fiber portion of a fiber;

removing a portion of fiber cladding of said selected fiber portion to form a fiber coupling surface spaced from a fiber core of said selected fiber portion within a reach of an evanescent field of a guided mode in said selected fiber portion; and

modifying a property of said selected fiber portion to increase a cladding refractive index of said selected fiber portion and hence to increase a spatial mode profile of said guided mode in said selected fiber portion to be greater than a spatial mode profile of said guided mode in an adjacent fiber portion whose cladding refractive index is not modified.

11. The method as in claim 10, wherein said selected fiber portion has a fiber cladding that is radiation sensitive, and where said modifying includes exposing said selected fiber portion to a radiation beam to increase said cladding refractive index.

12. The method as in claim 10, wherein said modifying includes implanting ions into the fiber cladding of said selected fiber portion.

13. The method as in claim 10, further comprising engaging said fiber coupling surface of said fiber to a fiber coupling surface of another fiber to cause evanescent coupling between the fibers.

14. The method as in claim 10, further comprising controlling said modification of said property to cause said cladding refractive index to change gradually along the fiber.

15. The method as in claim 14, wherein said cladding refractive index in said selected fiber portion is modified to be greater than a cladding refractive index of two fiber portions adjacent to said selected fiber portion but less than a core refractive index of said fiber at each location, and wherein said cladding refractive index of said selected fiber portion gradually decreases along said fiber from a center of said selected fiber portion towards two sides of said selected fiber portion and becomes equal to said cladding refractive index of said two fiber portions adjacent to said selected fiber portion.

16. A device, comprising:

a substrate having first and second opposing substrate surfaces and including an elongated groove formed over said first substrate surface; and

a fiber having a fiber coupling portion engaged in said elongated groove, a portion of fiber cladding of said fiber coupling portion being removed to form a side fiber surface spaced from a fiber core of said fiber within a reach of an evanescent field of a guided mode in said fiber;

wherein said fiber coupling portion has a fiber cladding portion whose radial index distribution is different from adjacent fiber portions to produce a radial mode profile wider than a radial mode profile of said adjacent fiber portions.

17. The device as in claim 16, wherein said substrate further includes a through hole between said first and said second substrate surfaces that penetrates through said substrate, said through hole located at one end of said elongated groove and one section of said fiber passing through said through hole to place another section of said fiber over said second substrate surface.

18. The device as in claim 16, further comprising a buffer layer in said elongated groove between said fiber and said substrate to reduce a stress between said fiber and said substrate.

19. The device as in claim 16, further comprising an optical grating formed in said fiber coupling portion.

20. The device as in claim 16, wherein a fiber cladding portion in said fiber coupling portion has a refractive index greater than a cladding refractive index of two fiber portions adjacent to said fiber coupling portion but less than a core refractive index of said fiber at each location, and wherein said refractive index of said fiber cladding portion in said fiber coupling portion gradually decreases along said fiber from a center of said fiber coupling portion towards two sides of said fiber coupling portion and becomes equal to said cladding refractive index of said two fiber portions adjacent to said fiber coupling portion.